Urethral pressure measurements have been used for more than 75 years to assess urethral closure function. Urethral pressure and urethral closure pressure are idealized concepts which aim to represent the ability of the urethra to prevent leakage. So long as the intraurethral pressure exceeds the proximal fluid pressure, urine cannot leak and therefore the subject should be continent. Measurement of urethral pressures requires the introduction of a catheter adapted to perform such measurements. A variety of different techniques are employed to make urethral pressure measurements. Moreover, in the field of urethral impedance planimetry, it is known to measure the elasticity or “tonus” of the urethra, the cross-sectional area of the urethra, bladder pressure, abdominal pressure and detrusor pressure. EMGs and imaging data may also be obtained when making such measurements.
One well known technique for assessing a patient's bladder function is PCA (or “Pressure Cross-Sectional Area”) catheter measurement as described, for example, in “A System for Measurement of Micturition Urethral Cross-Sectional Areas and Pressures” by Mortensen et al., Med. & Biol. Eng. & Comput., 1983, 21, 482–488; “Simultaneous Recording of Pressure and Cross-Sectional Area in the Female Urethra: A Study of Urethral Closure Function in Healthy and Stress Incontinent Women” by Lose in “Neurology and Urodynamics,” Volume 11, Number 2, 1992; and “Urethral Pressure Measurement Problems and Clinical Value” by Lose, Scand. J. Urol. Nephrol. Suppl. 207. See also “Urethral Impedance Planimetry” presented by Lose et al. at the Medtronic Satellite Symposium, ICS, Tampere, Finland, 2001.
FIG. 1 shows a prior art PCA catheter system 5 comprising catheter body 10, expandable and resilient balloon 20 mounted near distal end 30 of the catheter, balloon channel 40 for introducing saline solution 50 inside and removing saline solution 50 from balloon 20, distal micro-pressure transducer 60 mounted near distal tip 70 of catheter body 10, proximal micro-pressure transducer 65 mounted beneath a portion of balloon 20 and situated proximally from distal pressure transducer 60, and electrodes 80A, 80B, 80C and 80D mounted beneath balloon 20 on catheter body 10. Electrical connectors 9 at the proximal end of catheter system 5 permit electrical connections to be established between electrodes 80A through 80D, transducers 6Q and 65, or temperature or other sensors, and external recording and/or analysis equipment (not shown in the Figures).
Cross-sectional area (or “A”) is determined by delivering high frequency alternating current between excitation electrodes 80A and 80D and measuring the electrical conductivity of the saline solution inside balloon 20. Balloon 20 is then inflated and deflated incrementally with saline solution during rest and provocative maneuvers, and the drop in voltage between sensing electrodes 80B and 80D is measured. Using the field gradient principles described by Harris et al. in “Electrical Measurements of Urethral Flow” in “Urodynamics”, New York, Academic Press, Chapter 34, page 465, cross-sectional area A may be determined. The pressure inside balloon 20 may be increased incrementally to induce dilation, and the resulting pressures may be recorded using the proximal and distal pressure transducers. The resulting pressure response curve is a stress relaxation curve, which may be analyzed to determine the elastic properties of the patient's urethra. Balloon 20 is preferably fully distensible within the physiological range of the urethral cross-sectional area.
It will now be seen that PCA catheter system 5 comprises several expensive components, most notably distal micro-pressure transducer 60, proximal micro-pressure transducer 65, and electrodes 80A, 80B, 80C and 80D. In addition, catheter system 5 requires the incorporation of balloon channel 40 and the inclusion and mounting of balloon 20. Because the cost of a single PCA catheter system 5 may easily exceed several thousand dollars, it is preferable that at least portions of PCA catheter system 5 be reusable following sterilization.
To date, some PCA catheters have been re-used by mounting disposable balloons on catheter body 10 using sutures or ties 75 that are secured around the proximal and distal ends 85 and 90 of balloon 20. Mounting balloon 20 on catheter body 10 using such manual attachment techniques is time consuming, tedious and does not produce reliable seals between proximal and distal ends 85 and 90 of balloon 29 and the outside diameter of the catheter. What is needed is a PCA catheter system having a disposable balloon which may be readily and quickly mounted on or removed from a catheter body, and Which also provides a competent non-leaking seal between the balloon and the catheter when the balloon is filled with saline solution.
Patents and printed publications describing various aspects of the foregoing and other problems, as well as the state of the art, are listed below.    1. U.S. Pat. No. 4,023,562 to Hynecek et al. entitled “Miniature Pressure Transducer for Medical Use and Assembly Method.”    2. U.S. Pat. No. 4,191,196 to Bradley et al. entitled “Profilometry Method and Apparatus” to Ellis.    3. U.S. Pat. No. 4,545,367 to Tucci entitled “Detachable Balloon Catheter and Method of Use.”    4. U.S. Pat. No. 5,385,563 to Gross entitled “Urodynamic Catheter.”    5. U.S. Pat. No. 5,449,345 to Taylor et al. entitled “Detachable and Reusable Digital Control Unit for Monitoring Balloon Catheter Data in a Syringe Inflation System.”    6. U.S. Pat. No. 5,549,554 to Miraki entitled “Catheters Having Separable Reusable Components.”    7. U.S. Pat. No. 5,766,081 to Kreder entitled “Urethral Pressure Catheter.”    8. U.S. Pat. No. 5,779,688 to Imran et al. entitled “Low Profile Balloon-On-A-Wire Catheter with Shapeable And/Or Deflectable Tip and Method.”    9. U.S. Pat. No. 5,876,374 to Alba et al. entitled “Catheter Sleeve for Use with a Balloon Catheter.”    10. U.S. Pat. No. 5,919,163 to Glickman entitled “Catheter with Slideable Ballobn.”    11. U.S. Pat. No. 5,941,871 to Adams et al. entitled “Catheter Systems with Interchangeable Parts.”    12. U.S. Pat. No. 6,021,781 to Thompson et al. entitled “Intraurethral Pressure Monitoring Assembly and Method of Treating Incontinence Using Same.”    13. U.S. Pat. No. 6,136,258 to Wang et al. entitled “Method of Forming a Co-Extruded Balloon for Medical Purposes.”    14. U.S. Pat. No. 6,231,524 to Wallace et al. entitled “Pressure Device with Enhanced Fluid Monitoring Features.”
All patents and printed publications listed hereinabove are hereby incorporated by reference herein, each in its respective entirety. As those of ordinary skill in the art will appreciate readily upon reviewing the drawings set forth herein and upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, at least some of the devices and methods disclosed in the patents and publications listed hereinabove may be modified advantageously in accordance with the teachings of the present invention.